How do I burn the XBOX 360 Beta Games on the FTP to a disc?

Chances are you'll need a dual layer DVD which can hold up to 8GB.

The rar file is really weird though- no isos or anything

Well, what is the structure of the files?

For the beta games, you need a jtag-xbox or a development kit, if you have one of them you can put the game data on a usb-stick and run it directly from your xbox.

What is the minimal modding version requierment in the XBOX? I got 1.5, but I know that 1.54 is out..

You can inject them in to a USB flash drive like this guide explains: http://digiex.net/guides-reviews/consol ... drive.html

You do need a Jtag / Development kit however which im guessing you dont have. If you did you could just FTP the betas to the Xbox.